1. Field of the Invention
This invention relates to a milk flow meter for a milking system having a substantially stable vacuum level and more particularly relates to a milk flow device adapted to be positioned in a conduit between a milk claw and a pipe line for transporting in a selected direction and at a selected slope, assisted by gravity, a substantially continuous milk flow varying in height up to a maximum height within the conduit and wherein the maximum height is less than the height which would occlude the conduit and interrupt the vacuum level thereby enabling the milking system to maintain a substantially stable continuous vacuum while measuring milk flow.
2. Description of the Prior Art
Milking systems having a vacuum for performing milking of cows are well known in the art. Examples of such milking systems and controls therefor are described in several United States Patents, such as for example U.S. Pat. Nos. 5,896,827; 4,616,215; 4,605,040; 4,572,104; 4,516,530; 3,783,837 and 3,476,085
U.S. Pat. No. 5,996,529 discloses a milk metering and cow identification system which both monitors milk production and identifies each of a plurality of animals being milked. A host computer manages both the flow of data throughout the system and the operation of the milk metering subsystems. The system includes a flow meter comprising a upper housing member and a lower housing member which in use are sealably coupled with a baffle plate via spring clips. The baffle forms a function of reducing the turbulent, pulsatile fluid flow from a milk pump into a manageable fluid stream such that an accurate and reliable determination of milk flow rate can be obtain for a cow coupled to a milker.
U.S. Pat. No. 5,116,119 discloses a method and apparatus for measuring liquid flow which includes directing the liquid to flow through one or more flow channels while exposing the liquid to electromagnetic radiation. The apparatus measures the transparency to electromagnetic radiation of the liquid flowing through the flow channel and measures the momentary attenuation of electromagnetic radiation by liquid flowing through the flow channels to determine the momentary volume of the liquid flowing through the flow channel. This permits the apparatus to make a determination of the momentary flow rate of the liquid flowing through the flow channels.
A reference entitled MACHINE MILKING AND LACTATION by A. J. Bramley, F. H. Dood, G. A. Mein and J. A. Bramley, published by Insight books, Vermon, USA, describes the history, background and state of the art in milking systems and in Chapter 7 entitled Basic Mechanics and Testing of Milking Systems by G. A. Mein appearing at Pages 235 through 284, discloses and describes typical milking machine installations (the “Bramley et al. Reference”). The Bramley et al. Reference recognizes that controlling the maximum vacuum drop in the system is desirable because the vacuum drop depends on surface finish of pipes and the overall effective length, including bends and fittings of piping in the milking system and interference from various components such as milk flow meters.
It is known in the art that mastitis can occur if a milk blockage occurs within the inflation of a teat cup cluster causing a back flow of milk into the teat's orifice. Mastitis is an infection of animal body tissue within the mammary system of an animal. Mastitis may be caused by a number of other conditions including irritation to the teats, as is well known to persons skilled in the art. In a milking process, mastitis is generally caused by an introduction of foreign bacteria into the animal's udder, e.g. cow's udder, caused by severe irritation to the teats such that the teat orifices cannot be protected from environmental bacteria entering the teats. When mastitis occurs, it is an infection that the animal, e.g., cow's, body must counteract. Thus the animal's body energy is to be used to fight infection rather than produce milk.
A milking machine or milking system generally cause mastitis in two ways.
Mastitis is caused by application of damaging vacuum levels to the cows' teats which create a severe irritation. Since it is difficult to isolate with any degree of certainty at what level of vacuum such irritation occurs, the conservative approach is the least level of vacuum, the better. Each animal, such as a cow, reacts differently to vacuums being applied to teats and each animal tolerates various levels of vacuum differently.
When vacuum is applied to an animal's teats, a lower than atmospheric pressure exists within the animal's udder. When the animal gives milk faster than the milking system can transport the milk away from the teats resulting in a blocking or interfering with the vacuum, a flooding situation occurs resulting in the vacuum being blocked from the teats and udder. The udder is under the operating vacuum level equal to the source before the flooding occurs when flooding occurs, at an atmospheric pressure is bleed into the milk claw.
The vacuum level within the milk claw drops because flooding blocks the source of vacuum from the milk claw. This results in the loss of vacuum to the teats and udder. The udder seeks to return to the ambient atmospheric pressure from the original vacuum level. As a result, air will then fill the vacuum. The filling of the vacuum within the cow's udder causes a foreign air to be introduced into or drawn into the cow's udder. Air does not typically carry a detrimental amount of foreign bacteria, but air under a pressure differential functions as a propellant for bacteria. As such, air itself does not cause significant detriment to the health of the animals, e.g. cow, but the air may transport bacteria or other contaminants into the teats thereby contributing to mastitis.
If the vacuum seal breaks and water carrying bacteria is present around the udder, the water outside of or in the vicinity of the inflation and air at atmospheric pressure is drawn or sucked into the teats through the teat orifice.
To overcome such prior art, the inflations and milking systems have been designed to resist breakage of the vacuum seal and the outlet of milk claws and the entire milking system is sized to avoid interruption of the vacuum level. One such system is disclosed in U.S. Pat. No. 5,896,827.
Typically, animals, especially cows, are giving more milk at faster milk flow rates. The sizes and design of the state-of-the-art entire milking system are generally inadequate to handle the volume of milk without some degree of, and often severe, flooding. Also, known milk flow meter contribute to the flooding problems as discussed hereinbefore.
Flooding continually causes reverse pressure differentials and collapse of vacuum. The milk fluid, in effect, causes the average vacuum level within the claw, liners and teat end to be much lower than the desired vacuum level due to continual flooding which interrupts the vacuum and causes undesired pressure differences on the teats.
Introduction of known milk flow meters into vacuum controlled milking systems contribute to interruption of the vacuum in such system for the following reasons.
Prior art milk flow meters do not have a cross-sectional area sufficiently large to pass a continuous milk flow without occluding thereby contributing to flooding and interruption of the vacuum.
A milking system including a milk quantity meter is disclosed in U.S. Pat. No. 5,792,964. In one embodiment of a milk quantity meter disclosed in U.S. Pat. No. 5,792,964, the milk quantity meter is located between a teat cup and a buffer vessel, such as a milk glass, to measure a pulsating milk stream from an individual teat which is obtained pulsationwise and depending on the pulsation frequency at which the milking takes place thereby measuring the quantity of milk obtained from separate udder quarters of the animal.
In U.S. Pat. No. 5,792,964, the milk quantity meter measures the milk flow by integrating the pulses of milk in the fully occluded conduit between the teat cup and milk vessel. The milk quantity meter includes three electrically conductive elements, two of which measure the resistivity of the milk filling the conduit and a third electrode measures the conductivity of the milk. The pulsed milk flow is determined by the area of the conduit filled by the milk and the time required for a milk pulse, which fills the entire conduit, to travel between the two electodes.
In a second embodiment of a milk quantity meter disclosed in U.S. Pat. No. 5,792,964, the milk quantity meter is located in the pipeline between the buffer vessel, such as a milk glass, and a milk tank. The buffer vessel is used to effectuate a separation between the air and milk. The total quantity of milk can be determined accurately by means of only one quantity meter by discharging the milk from the buffer vessel to the milk tank in one single pulsation wherein the quantity meter is obviously fully occluded by the milk filling the meter due the maximum flow arising from a single pulsation of milk.
Apparatus for use in monitoring milk flow to control removal of teat cups from an animal at the termination of a milking cycle is disclosed in UK Patent Application 2 124 877 A. The monitoring apparatus is located between a cluster having teat cups and a flexible milk flow tube. During milking, a slug of milk occupies the entire cross-section of the path and monitoring apparatus. As the end of the milking cycle is reached, the quantity of milk in the path decreases and is monitored by two electrodes which measures the resistance of the milk within the path and generates an output signal which decreases in amplitude as the level of milk in the path decreases. The monitoring device's responsive to a significant fall in amplitude of the output signal to provide a signal which initiates removal of the teat cups mechanically from the teats of the animal.
Flow meters for measuring flow of milk or fluid utilizing measurement of fluid conductivity or specific resistance is known in the art and examples of apparatus are disclosed in U.S. Pat. Nos. 5,245,946; 4,922,855; 3,989,009 and 3,242,729.
It is also known in the art of flow meters to utilize flow-measuring devices to shut off systems such as milking systems upon completion of a milking cycle. Typical apparatus and systems for controlling shut off of equipment including milking systems is disclosed in U.S. Pat. Nos. 5,996,529, 4,756,274 and UK Patent Application 21248772 discussed hereinbefore.
Milk flow meters utilizing metering chambers are well known in the art and typical systems are disclosed in U.S. Pat. Nos. 5,720,236; 4,433,577; 4,112,758 and DES 357,877.
Apparatus for measuring milk flow utilizing elongated measuring chambers are disclosed in U.S. Pat. Nos. 5,116,119, 4,574,736 and 2,898,549.